AV Referendum: David Cameron will have to campaign for a 'Yes' vote

Smart move on Nick Clegg's part to insist that the referendum on AV be held next May. He knows that the sooner it's held, the more pressure David Cameron will be under to campaign for a "Yes" vote. Why? Because if the outcome of the referendum is "No", the coalition probably won't survive and Cameron can't afford for it to collapse so soon.

Agreeing to hold a referendum on AV was the big concession the Conservative negotiating team made in order to secure the support of the Lib Dems. Nick Clegg and his Orange Book colleagues may have been willing to throw in their lot with the Tories willy nilly, but they wouldn't have been able to take their party with them without the promise of a referendum. And the reason it means so much to the Lib Dems is because they believe there's a real chance the public might vote "Yes". If those hopes are dashed, Clegg is going to have a devil of a job persuading his party to remain in the coalition, particularly as the Lib Dems' standing in the opinion polls has plummeted since May 6.

Cameron now has the tricky task of going back on his pledge to campaign for a "No" vote, something he's unlikely to do before the referendum bill has made its way through Parliament. After all, his own back benchers are more likely to rebel if they think he's going to start campaigning for a "Yes" vote. Factor in the opposition of the Parliamentary Labour Party – a real possibility since it will make Cameron's life more difficult – and there's a danger the referendum bill will be defeated.

Assuming the bill is passed, Cameron will have no choice but to change his position. One option will be to remain steadfastly neutral, refusing to campaign for a "Yes" or a "No" and encouraging his own MPs to follow their consciences. But that would look a bit weak. Better to bite the bullet, campaign for a "Yes" vote alongside Nick Clegg, and then reap some of the political reward if AV is adopted. His pretext for doing this will be that he's changed his mind about the effectiveness of coalition government. Yes, AV is more likely to lead to hung parliaments, but the past year has taught him that coalition government is no bad thing.

How will Cameron's back benchers react to this betrayal? Incandescent rage, I expect. They will say they were hoodwinked into supporting the coalition and had they known it would lead to the abandonment of their beloved electoral system they never would have done so. But Cameron will be able to cope more easily with a rebellion in his own ranks than a rebellion among the Lib Dems, not least because he can depend upon the great Tory virtue of party loyalty. In any event, the rebels will have nothing to gain from defeating the coalition. The AV vote will have been lost and forcing an early election will not bring back the old electoral system.

Whatever Cameron does it will be a gamble – and Nick Clegg has raised the stakes by railroading him into holding the referendum in less than a year's time. In order to survive, Cameron will need all his political wits about him.